1. Field of the Invention
This invention relates generally to hermetically sealed compressors, and more particularly to small hermetically sealed refrigeration compressors, used in household appliances such as refrigerators and food freezers.
2. Description of Prior Art
Because of high energy costs and various governmental requirements, household appliances are being extensively redesigned to increase their energy efficiency. In the case of refrigerators, substantial improvements have been made by various improvements of the refrigeration system itself, including improvements in the size of evaporators and condensers. One of the objectives that has received the most attention is to increase the efficiency of refrigeration compressors. Increases in compressor efficiency have come primarily from increases in the electrical efficiency of motors which drive the compressors and from increases in pump volumetric efficiency. Decreasing the bearing friction of a principal rotating part, such as a crankshaft, in such compressors, will also contribute to increasing the efficiency of a refrigeration compressor.
A conventional hermetically sealed compressor of the type referred to above, for use in household appliances such as refrigerators, is described here with reference to FIG. 7 (as also disclosed in Japanese Laid-open Patent Applications No. 63-5186). In FIG. 7, electric element 1 and compression element 2 are generally resiliently supported within and in spaced relationship to hermetic container 3. Electric element 1 comprises stator 4, rotor 5, and crankshaft 6. Rotor 5 is pressed in place on crankshaft 6. Ball bearings 7, 8 are securely positioned at both upper and lower ends of bearing hub 9 to support the weight of rotor 5 and crankshaft 6. At its lower end, crankshaft 6 carries an eccentric axial part 10, which is integrally formed in a single molding with crankshaft 6. Eccentric axial element 10 fits within one end of connecting rod 11 and the other end of connecting rod 11 is connected to piston 12 which is slidably positioned within cylinder 13. In the above-described structure, in operation, the compressor is driven by stator 4 and rotor 5 powered by connection with a source of electrical energy (not shown) and piston 12 is reciprocated in cylinder 13 to compress refrigerant gasses.
However, this conventional hermetically sealed compressor may have some collateral disadvantages which include:
(a) Because of a cantilever structure, that is, both ball bearings 7 and 8 are installed at the same side in regard to the axis of cylinder 13, ball bearings 7 and 8 are heavily loaded in operation. FIG. 8 shows a schematic force diagram of ball bearings 7, 8 as they are loaded in operation. W is a reaction force to the compression action. L is the distance between ball bearing 8 and axis 13A of cylinder 13. K is the distance between ball bearings 7 and 8. J is the distance between bearing 7 and axis 13A of cylinder 13. As shown in FIG. 8, ball bearing 7 is pressed by the force of W.multidot.L/K which is larger than W in the direction shown by arrow A. Ball bearing 8 is also heavily pressed by the force of W.multidot.J/K in the direction shown by arrow B. Accordingly, the above-described structure may cause a reduction in the life span of both ball bearings 7 and 8, and it may be very difficult to assure the reliability of such a structure.
(b) In general, it is necessary to pressurize both ball bearings 7 and 8 (i.e. hold them under pressure against the crankshaft) in order to assure the reliability and reduce the noise of a structure as shown in FIG. 7. In this conventional hermetically sealed compressor of FIG. 7, though ball bearing 8 is pressurized by the deadweight of compression element 2, it is necessary to pressurize ball bearing 7 by additional means which increases the number of parts required.
(c) In this structure, because of the radial clearance required (particularly as bearings wear), it is necessary to provide a space S in view of assembly clearance dimensions between stator 4 and rotor 5. The space S may make compressor operation unstable and also cause a reduction in motor efficiency.